Acid hardening fixing bath



PATENT; OFFICE ACID HARDENING FIXING BATH Harold D. Russell, Rochester, is. m, assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New York No Drawing. Application September 27, 1932, Serial No. 635,060

2 Claims. (Cl. 95-88) This invention relates to photographic acid hardening fixing baths and particularly to novel compositions for the purpose containing compounds of boron.

I have discovered a group of compounds of boron which are of great advantage in acid hardening fixing baths and have also made certain useful observations concerning the composition of acid hardening fixing baths containing these substances.

The compounds of boron which I use are the soluble salts 'of the oxygen acids of boron and the esters of these acids, especially the esters of boric acid, or the acids themselves. The

' esters include particularly such substances as boron triacetate, glycol borate, phenyl borate and the glyceryl esters of boric acid. One of the glyceryl esters is manufactured and sold conimercially under the name glycryl bori-borate. These substances are compounds resulting from the interaction of glycerin and boric acid or borax and while their composition is not exactly known they are understood to be glyceryl esters of boric acid, probably in varying mixtures and proportions.

A number of oxygen acids of boron are known, the soluble salts of any of which would be useful in my invention. The alkali (sodium and potassium particularly) salts are nearly all soluble, cheap and eflicient. Among the oxygen acids of boron the compounds of which I may use are:

It is understood that any of these acids of themselves may also be employed.

The addition of one of the salts or esters of these boron acids to an acid hardening fixing bath, such, for example, as one containing potassium alum and acetic acid, extends the pH range over which hardening takes place and raises the pH value at which sludging occurs. It is, of course, well known that as an acid hard-- ening fixing bath is subjected to more and more use, the acid in it gradually becomes neutralized by the alkaline developer carried over by the photographic plates, films, or paper. The pH of the solution accordingly rises. Satisfactory hardening with the usual hardening agents, such as ordinary alum, occurs only during a certain range of pH values. As the pH of the solution increases beyond this useful range, the bath ceases to exert much hardening.

At the same time, as the bath becomes more alkaline and the pH value rises, a precipitate begins to be thrown down and this phenomenon is commonly known as sludging, since the precipitate slowly accumulates in the bottom of the tray or tank as a very finely divided sludge. The bath may also become more or less cloudy. This precipitate or sludge probably consists of basic aluminum sulfite, aluminum hydroxide or aluminum oxide, either singly or in mixture, depending on conditions. The boron compounds which I employ raise the pH value at which sludging occurs. These compounds therefore have a very useful eflect in prolonging the life of the fixing bath and result in convenience and economy since it is not necessary to replace the fixing bath so soon.

The following formulas are illustrative embodiments of my invention:

1. Sodium thiosulphate 300 grams Sodium sulfite (desiccated) 15 grams Propionic acid 20 grams Potassium alum 15 grams Boric acid 5 grams Water to 1 liter 2. Sodium thiosluphate 300 grams Sodium sulflte (desiccated) 15 grams Acetic acid 15 c. c. Potassium alum 15 grams Glycol borate 10 grams Water to 1 liter 3. Sodium thiosulphate 300 grams Sodium sulfite (desiccated) 15 grams Boron triacetate 15 grams Potassium alum 15 grams Water to 1 liter 4. Sodium thiosulphate; 300 grams Sodium sulfite-' 15'grams Acetic acid 15 0.0. Citric acid L 1 gram Potassium alum 15 grams Boric acid 5 grams Water to 1 liter 5. Sodium thiosulphate 300 grams Sodium sulfite 5 grams Acetic acid 20 0.0.

Sodium acetate 20 grams Potassium alum 20 grams Borax 20 grams Water to 1 liter The above formulas are all complete acid hardening fixing baths which are'useful for either positive or negative material.

It is usually desirable to have present in such a fixing bath an organic acid, such as acetic acid. I have found that propionic acid and butyric acid may be substituted for the acetic acid or their soluble salts may be used iI other acids are present. Boron triacetate may be substituted for.

both the acetic acid and the boron compounds.

Certain fixing baths may be compounded in which a mineral acid is used with the borate ion and the acetate ion. Such an example is the following.

Formula 6 Sodium thiosulphate 800 grams Sodium sulphite anhydrous 15 grams Sodium acetate anhydrous 20 grams I Boric acid grams Sulphuric acid conc 5 c.c.

Alum grams Water to 1 liter I have also found that the sludging tendency of a given bath maybe decreased by increasing the concentration of the acid ion such, for example, as the acetate ion, or by increasing the concentration of the boron compound or the borate ion. The addition 01' small quantities of other acids, such as citric, tartaric, fumaric,

malic, maleic, lactic, glycolic, and glycero-phosphoricacids is also efiective in decreasing the sludging tendency. These other acids are normally employed in rather small quantities in fixing baths contai'ningpotassium alum, as relatively large quantities of these acids decrease the hardening properties of such a bath.

The boron compounds which I have mentioned,

in common with most boron compounds that are soluble in water, decompose to give boric ac d in solution. Solutions containing these compounds may therefore be said to containboric acid or the borate ion. I

The term salt of an oxygen acid of boron is intended to include the inorganic true salts and also the organic compounds or esters.

It will be evident that a large numoer of acid hardening flxing baths of difierent proportions and constitutions may be compounded in accordacetate, glycol borate, phenyl borate and the glyceryl esters of boric acid and an acid selected from the group consisting of citric acid, tartaric acid, fumaric acid, malic acid, maleic acid, lactic acid, glycolic acid and glycero-phosphoric acid.

HAROLD D. RUSSELL. 

